The invention relates to a turbo-code decoder and a turbo-code decoding method with iterative channel parameter estimation, in particular for the mobile radiotelephone field.
In recent times, binary parallel-concatenated, recursive, systematic convolution codes, referred to as turbo codes, have been used for channel coding. Substantially improved error protection can be achieved by using turbo codes instead of convolution codes, in particular for transmitting large blocks of data bits. The idea on which the turbo code is based entails the concatenation of at least two binary, recursive, systematic convolution coders (RSC coders) using turbo-code interleaving devices. The RSC coders generate redundant data strings. The coding is interleaved by the coders in blocks in the turbo coder. The output data string of the turbo coder contains the original input data string an systematic information, and in addition, the redundant data as non-systematic information. The structure of a conventional coder is described in detail, for example, in xe2x80x9cAnalyse und Entwurf digitaler Mobilfunksystemexe2x80x9d [Analysis and design of digital mobile radio systems] by Dr. Peter Jung, Teubner Verlag, Stuttgart, 1997, pp. 334-348.
The turbo-coded data are output by a transmitter and are forwarded via a data channel to a receiver that contains a turbo-code decoder. The turbo-code decoder reverses the coding performed in the turbo coder and outputs estimated received data values that are intended to correspond as closely as possible to the original data string coded by the turbo-code coder. However, the data transmission channel or channel path is not stable, but is subject to fluctuations. Using the received data, it is possible to estimate the channel condition of the data transmission channel. Specific channel parameters are determined here. The more accurate the estimate of the transmission channel condition, the lower the bit error ratio will be.
FIG. 1 shows a prior art turbo-code reception circuit.
The turbo-coded received data contain systematic information data x and redundant data y. The coded received data are fed to an equalizer that outputs the equalized turbo-coded received data to a circuit for channel parameter estimation, which weights the equalized turbo-coded received data depending on the determined channel parameters and outputs them to a turbo-code decoder. The turbo-code decoder forwards the turbo decoding of the weighted, systematic and redundant received data and outputs an estimated value data string for further data processing.
The problem with the arrangement shown in FIG. 1 is that only one channel parameter estimation is carried out for each received data block by the circuit that is used for channel parameter estimation and weighting of the received data. However, since the transmission channel can fluctuate severely, particularly in the mobile radio field, due to the effects of interference, the determined estimated channel parameter values are so inaccurate that they produce an inadequate system response when used in the turbo-code decoder, thereby increasing the bit error rate.
It is accordingly an object of the invention to provide a turbo-code decoder and a turbo-code decoding method which overcome the above-mentioned disadvantages of the prior art apparatus and methods of this general type.
In particular, it is an object of the invention to provide a turbo-code decoder and a turbo-code decoding method in which the channel parameters are iteratively and continuously re-estimated in order to respond quickly to fluctuations in the transmission channel, and thus to reduce the bit error rate.
With the foregoing and other objects in view there is provided, in accordance with the invention, a turbo-code decoder with iterative channel parameter estimation for decoding turbo-coded received data that includes systematic information data and redundant data. The turbo-code decoder includes: a weighting circuit for weighting turbo-coded received data with at least one estimated channel parameter; a first channel decoder for generating reliability information data depending on received systematic information data, a first redundant data string, and a de-interleaved extrinsic information data string; a turbo-code interleaver for interleaving the reliability information data to obtain interleaved reliability information data; a second channel decoder for generating an extrinsic information data string and probability ratio data, the extrinsic information data string and the probability ratio data being generated depending on the interleaved reliability information data and a second redundant data string; a first turbo-code de-interleaver for de-interleaving the extrinsic information data string to obtain the de-interleaved extrinsic information data string, the de-interleaved extrinsic information data string being fed back to the first channel decoder; a second turbo-code de-interleaver for de-interleaving the probability ratio data to obtain de-interleaved probability ratio data, the second turbo-code de-interleaver outputting the de-interleaved probability ratio data; a threshold value decision circuit for generating estimated value data from the de-interleaved probability ratio data; a turbo-code coding circuit for turbo-coding the estimated value data to obtain turbo-coded estimated value data; and a comparison circuit that, depending upon a result of a comparison of the turbo-coded estimated value data with the turbo-coded received data, iteratively sets the at least one estimated channel parameter for weighting the turbo-coded received data.
In accordance with an added feature of the invention, there is provided, a data-separation device for separating the received data into the received systematic information data, and a plurality of redundant data strings which include the first redundant data string and the second redundant data string.
In accordance with an additional feature of the invention, the data-string separation device includes a multiplexer that outputs the first redundant data string to the first channel decoder and that outputs the second redundant data string to the second channel decoder.
In accordance with another feature of the invention, a buffer memory buffer stores the second redundant data string.
In accordance with a further feature of the invention, the turbo-code coding circuit includes RSC coders, puncturing devices configured downstream from the RSC coders, at least one turbo-code interleaving circuit, and a multiplexer.
In accordance with a further added feature of the invention, the estimated channel parameter is the signal-to-noise ratio.
With the foregoing and other objects in view there also is provided, in accordance with the invention, a decoding method for decoding turbo-coded received data. The method includes steps of: weighting turbo-coded received data with at least one estimated channel parameter; generating reliability information data depending on received systematic information data that is contained in the received data, a first redundant data string that is contained in the received data, and a sequence of extrinsic information data; interleaving the generated reliability information data; generating the extrinsic information data depending on interleaved reliability information data and a second redundant data string; generating probability ratio data depending on the interleaved reliability information data and the second redundant data string; de-interleaving the probability ratio data to obtain de-interleaved probability ratio data; forming an estimated value data string from the de-interleaved probability ratio data by performing a threshold value decision; turbo-coding the estimated value data string to obtain turbo-coded estimated value data; comparing the turbo-coded estimated value data with the turbo-coded received data; and iteratively setting the at least one estimated channel parameter to weight the turbo-coded received data depending on a comparison between the turbo-coded estimated data and the turbo-coded received data.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a turbo-code decoder and a turbo-code decoding method with iterative channel parameter estimation, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.